Often, the Church Year is divided into two approximate halves. The "festival half," sometimes (rather inappropriately, in my opinion) termed "the Lord's half year," runs from the First Sunday in Advent through the week following Pentecost. This period encompasses all of the major Christological observances. Trinity Sunday is sometimes considered the close of the festival half but is usually understood to be the beginning of the non-festival half, sometimes called "the Church's half year." Its proper liturgical color is white, but except for certain special observances, green will be used for paraments and vestments until the church year closes.

This day celebrates the mystery of the Holy Trinity, Father, Son, and Holy Spirit — One God yet Three Persons — a fact revealed in Scripture but apprehended only by faith, since its comprehension defies human logic. Some people with a literalistic (rather than literal) understanding of the Bible attempt to deny this doctrine since they cannot find "Trinity" or "Triune" or "Three Persons" in the pages of Scripture. However, the sum total testimony of the Old and New Testaments certainly speaks of God as One yet also as Three Persons.

Regardless of the lectionary cycle used, the appointed Scriptures for the day reflect both God's undivided unity of self and His Triune nature. While not often used by most of the Christian Church during the rest of the year, much of the Western Church uses the Athanasian Creed as its confession of faith on Trinity Sunday.

Almighty and everlasting God, You have given us grace to acknowledge the glory of the eternal Trinity by the confession of a true faith and to worship the Unity in the power of the Divine Majesty. Keep us steadfast in this faith and defend us from all adversities; for You, O Father, Son, and Holy Spirit, live and reign, one God, now and forever.